This invention relates to imaging members and their preparation by imagewise application of a fluid to a clay-containing fluid receiving element. The invention also relates to a method of using the imaging members for lithdgraphic printing.
The art of lithographic printing is based upon the immiscibility of oil and water, wherein the oily material (or ink) is preferentially retained by image areas on a substrate. When a suitably prepared surface is moistened with water and ink is applied, certain areas retain the water and repel the ink, and other areas accept the ink and repel the water. Ink can then be transferred to the surface of a suitable receiving material, such as cloth, paper or metal, thereby reproducing the image. Commonly, the ink is transferred to an intermediate material known as a blanket that in turn imagewise transfers the ink to the surface of the receiving material upon which the image is to be reproduced.
Conventional lithographic printing plates typically include a hardenable polymeric layer (usually visible or UV light-sensitive) on a suitable metallic or polymeric support. Both positive- and negative-working printing plates can be prepared in this fashion. Upon exposure, and perhaps post-exposure heating, either imaged or non-imaged areas are removed using wet processing chemistries.
Thermally sensitive printing plates are also known. They include an imaging layer comprising a mixture of dissolvable polymers and an infrared radiation absorbing compound. While these plates can be imaged using lasers and digital information, they require wet processing using alkaline developers to provide the printable image.
Many different types of digitally controlled imaging or printing systems are known. These systems utilize a variety of actuation mechanisms, marking materials and recording media. Examples of such systems include, but are not limited to, laser electrophotographic printers, LED electrophotographic printers, dot matrix impact printers, thermal paper printers, film recorders, thermal wax printers, dye diffusion thermal transfer printers, and ink jet printers. Due to various disadvantages or limitations, such digital printing systems have not significantly replaced mechanical printing presses and the more conventional printing plates described above, even though these older systems are labor intensive and inexpensive only when more than a few thousand copies of the same image are wanted. Yet, there is considerable activity in the industry to prepare media that can be digitally imaged and used to provide high quality, inexpensive copies in either a short or long printing job.
Ink jet printing has become recognized as a viable alternative in the industry because of its non-impact deposition of ink droplets, low-noise characteristics, its use of common receiving materials, and its avoidance of toner transfer and fixing (as in electrophotography). Ink jet printing mechanisms can be characterized as either continuous ink jet or xe2x80x9cdrop on demandxe2x80x9d ink jet printing. Various ink jet printers and systems are currently available for a number of markets, including their common use with personal computers. A very essential aspect of such systems, of course, is a printing ink that has all of the necessary properties for a given application.
The use of ink jet technology to provide lithographic printing plates has been shown in the trade on a number of occasions, including the Print ""97 trade show in Chicago, September, 1997 (for example by Iris Graphics, Inc.). Various early publications about such technology including nozzles and drop modulation include U.S. Pat. No. 1,941,001 (Hamsell), U.S. Pat. No. 3,373,437 (Sweet et al), U.S. Pat. No. 3,416,153 (Hertz et al), U.S. Pat. No. 3,878,519 (Eaton), and U.S. Pat. No. 4,346,387 (Hertz).
Printing plates made using ink jet printing are also described in U.S. Pat. No. 4,003,312 (Gunther), U.S. Pat. No. 4,833,486 (Zerillo), U.S. Pat. No. 5,501,150 (Leenders et al), U.S. Pat. No. 4,303,924 (Young), U.S. Pat. No. 5,511,477 (Adler et al), U.S. Pat. No. 4,599,627 (Vollert), U.S. Pat. No. 5,466,658 (Harrison et al), and U.S. Pat. No. 5,495,803 (Gerber et al).
JP Kokai 53-015905 describes the preparation of a printing plate by ink jet printing using ink comprising an alcohol-soluble resin in an organic solvent onto an aluminum support. Similarly, JP Kokai 56-105960 describes ink jet printing using an ink comprising a hardening substance, such as an epoxy-soybean oil, and benzoyl peroxide, or a photohardenable polyester, onto a metallic support. These inks are disadvantageous in that they include light-sensitive materials or environmentally unsuitable organic solvents. EP-A-0 776,763 (Hallman et al) describes ink jet printing of two reactive inks that combine to form a polymeric resin on a printing plate. JP Kokai 62-25081 describes the use of oleophilic ink jet ink.
Inks for high-speed ink jet drop printers must have a number of special characteristics. Typically, water-based inks have been used because of their conductivity and viscosity range. Thus, for use in a jet drop printer the ink must be electrically conductive, having a resistivity below about 5000 ohm-cm and preferably below about 500 ohm-cm. For good fluidity through small orifices, the water-based inks generally have a viscosity of from 1 to 15 centipose at 25xc2x0 C.
In addition, in recent years, the drop size of inks applied by ink jet printing has become smaller resulting in higher resolution and quality images, but the smaller drop size requires smaller nozzles for application. These smaller nozzles are more likely to become partially or wholly plugged from dried ink and deposits, thereby affecting the size and accuracy of drop placement.
Beyond this, the inks must be stable over a long period of time, compatible with ink jet materials, free of microorganisms and functional after printing. Required functional characteristics include resistance to smearing after printing, fast drying on paper, and being waterproof when dried.
While the teaching of the art provides some solutions to these problems, there is a continuing need for an improved means for preparing imaging members (such as lithographic printing plates) using ink jet printing in order to provide accurate and high quality images.
This invention provides an imaging method comprising:
A) imagewise applying a fluid to a fluid receiving layer of a fluid receiving element, the fluid receiving layer comprising clay, a water-soluble binder and a hardening agent, the fluid comprising an aqueous solution of a silane having two or more hydroxy, alkoxy or acetoxy groups.
Thus, this invention also includes an imaging member provided by the imaging method described above.
In additional embodiments of the invention, the noted method further includes the steps of:
B) contacting the image on the fluid receiving element with water or a fountain solution and ink, and
C) imagewise transferring the ink to a receiving material.
One advantage of this invention is that a durable imaging member can be prepared quickly and effectively using ink jet printing without the necessity of heating or additional treatment (although such heating and treatment can be used if desired). The resulting printing members can be used to provide images with good discrimination and high quality. The fluid used in the method has low viscosity and thus minimizes the possibility of plugging of ink jet printing heads. Moreover, the fluid is rapidly dried or cured to form a water-insoluble matrix in the fluid receiving layer that is partially composed of clay. This layer quickly absorbs the fluid so there is little fluid spreading that would reduce image discrimination.
It was surprising that the specific fluid used in the present invention could be used in combination with the specific fluid receiving element described herein to provide an imaging member that provides highly accurate and high quality printed images.